1. Field of the Invention
The invention concerns prosthetic knee joint devices.
2. Description of the Related Art
Various devices have been proposed in the past in attempting to provide a knee joint prosthesis which permits simulation of the natural joint function. Patent specification GB 1,534,263 describes a joint device referred to commonly and in this specification as a meniscal device which comprises femoral, tibial and meniscal components co-operable to allow congruence of the interfacing articulation surfaces while allowing close simulation of the natural joint in flexion-extension. Such devices can employ components of unicompartmental, bicompartmental or, in the case of the femoral component, tricompartmental form. The contents of patent specification GB 1,534,263 are included herein by reference.
In the case of the basic meniscal device, the joint components themselves offer no constraint against their mutual separation; freedom of movement being allowed under the control of the related soft tissues, which generally ensure that the meniscal component is retained in the desired manner between the associated components and cannot therefore dislocate. In some cases, however, it is appropriate to provide means to prevent or at least reduce the risk of dislocation of the meniscal component and some forms of the device have been developed to provide a mechanical coupling between the meniscal and tibial components with a view to ensuring the avoidance of dislocation. Patent specification GB 2,245,175 describes such a device, in which means are provided, separably connectable with the tibial component, to at least partially bridge the associated meniscal component to retain their interengagement. Other proposals have been put forward which feature some form of interengagement between a bicompartmental tibial component and a bicompartmental meniscal component, such as those described in EP-A-0 546 726 and EP-A-0 519 872.